Big-spending PSG, five-time champion Barcelona and Jose Mourinho's Manchester United are among the teams looking to book a Champions League last-16 place Tuesday.
The pick of the action sees Anderlecht take on Neymar and Co in Paris, while Barcelona face Olympiakos and Roma go head-to-head with Chelsea in Italy.
Here we take a look at what is at stake in each group:
Man Utd v Benfica
Mourinho's side can secure a place in the last 16 with two matches to spare with a win at Old Trafford, if Basel avoid defeat against CSKA Moscow.
Basel v CSKA
Basel will clinch a spot in the knockout phase with a second straight win over CSKA, if Benfica fail to beat United.
Celtic v Bayern
Brendan Rodgers' team face a stiff test against Bayern Munich as they bid to keep their European adventure alive.
PSG v Anderlecht
Unai Emery's French heavyweight have cruised through their opening three fixtures - netting 12 goals with none conceded - and will be expected to again sweep aside Anderlecht at Parc des Princes.
Atletico v Qarabag
Diego Simeone's Atletico Madrid are still searching for their first win of the competition after a goalless draw in Azerbaijan a fortnight ago.
Chelsea v Roma
The winner of the clash at the Stadio Olimpico will be well-placed to reach the last 16 with both teams still to play a game against struggling Qarabag.
Olympiakos v Barca
The first meeting two weeks ago saw Barca ease to a 3-1 win with only 10 men, while Olympiakos, bottom of Group D, will be eliminated if they lose and Sporting Lisbon fail to beat Juventus.
Sporting v Juve
Sporting and Juve look set to be in a straight fight for second place in Group D behind Barca, with today’s match in Lisbon crucial after the Italians' 2-1 win at Turin.